Presplitting device



Oct. 31 1967 J. 5. WILSON PRESPLITTING DEVICE Filed Jan. 21,

INVENTOR. Jo/1n 6. M/i/son BY; 2 fiTTOR/Vfy 3,349,705 PRESPLITTING DEVICE John S. Wilson, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed Jan. 21, 1966, Ser. No. 522,077 8 Claims. (Cl. 102-24) ABSTRACT OF THE DISCLOSURE An explosive article having one or more strands of a cap-sensitive explosive spaced at predetermined distances on the periphery of a sheath of flexible material. This article is particularly adapted for use in boreholes to fracture surfaces along predetermined cleavage lines. The article is made by securing a plurality of explosive strands spaced apart between two films of confining material, either through heat sealing or use of an adhesive.

This invention relates to an explosive article for presplitting a solid formation, such as rock, with multi le strands or cords of explosives spaced at predetermined distances from each other the periphery of a sheath, and to a method for manufacture of the article, and more particularly pertains to an explosive article which has two or more strands or cords of explosive spaced from each ther at a predetermined distance or angle around the periphery of a non-explosive, flexible sheath, and to a method of manufacturing the article by interposing each strand of the explosive between layers or webs of the flexible sheath material at predetermined distances along the periphery of the explosive article or by adhesively securing the strand to the sheath.

Cutting blocks of stone, such as limestone, granite and marble, from a solid face is practiced currently by boring a row of 2 to 3 inch diameter holes spaced a few feet apart, placing two strands of Primacord into each hole, filling the hole with sand and detonating the Primacord. If the strand is properly aligned and is not moved during the stemming with sand, and if the borehole is nearly perpendicular, satisfactory results can be obtained. Too frequently, one or more of the conditions specified above is not attained, so that fractures occur along some undesired line. This results in the production of blocks of undesired dimensions which often require expensive trimming operations to be marketable or the blocks are converted to scrap.

One advantage of this invention is the simplicity with which proper alignment of the explosive strand along the desired line of fracture can be attained. Another advantage is the low cost of attaining this alignment. In addition, the article can be manufactured by heat sealing the strand of explosive between layers of flexible film or by the use of an adhesive to bond the explosive strands at spaced distances on the periphery of the sheath.

The preferred form of the invention is shown in the drawing wherein: FIGURE 1 is a perspective view of one form of the explosive article. FIGURE 2 is a top view of the explosive article positioned in a borehole, and FIG- URE 3 is a schematic view of a method for making the article.

Referring to the drawing in FIG. 1, 10 is a sheath of flexible material which can be metal foil, a thermoplastic sheet, preferably one which is heat sealable, a cellulosic material or a proteinaceous material. Representative metal foils are aluminum or iron. Exam les of thermoplastic sheets are known homopolymers and copolymers of polymerizable monoolefinically unsaturated compounds such as styrene, a-methyl styrene, ring alkylnited States Patent 3,349,75 Patented Oct. 31, 1967 ated or halogenated styrene, acrylonitrile, ethylene, propylene, the butylenes, vinyl esters both organic and inorganic esters, such as vinyl acetate, propionate or other organic acid, vinyl halides, particularly vinyl chloride, vinylidene halides, esters of acrylic and methacrylic acids, copolyrners of maleic anhydride and maleic esters, vinyl ketones, vinyl ethers, rubber, either natural or synthetic, cellulose esters, such as cellulose acetate, cellulose butyrate, cellulose acetate-butyrate, and cellulose propionate, water-insoluble cellulose ethers and the various known polyester films. The preferred thermoplastics are the heat scalable styrene containing polymers, polyethylene and polyvinyl chloride. Typical cellulosic materials include paper which can be coated with a wax, asphalt, tar, resin or other water proofing ingredient, regenerated cellulose and textile materials made from cotton, sisal, istle or hemp fibers.

The sheath 10 is heat sealed or adhesively bonded at its outer edges 11, 11' and at a space 12, 12 inwardly from the outer edge, to provide pockets or cells 13, 13' for the explosive strands 14, 14. Between the inner sealed or bonded areas 12, 12' is an open space 15, defined by walls 16, 17. The space 15 can be filled with stemming when the device is placed in position in a borehole prior to detonation.

The explosive strands or cores 14, 14, can be any cap sensitive material which can be extruded, molded or cast. Representative materials of this type include Primacord, i.e. usually 200 grain Primacord is preferred, cloth or plastic bound TNT, pentolite, RDX including C-C type, tetry'l or lea-d bound TNT, cyclotol or composition B.

Adhesives when used to make the explosive article can be carbohydrate based, rubber base, protein base or synthetic resin base, and can be used as melts, if they soften at low enough temperatures, as aqueous solutions or emulsions, or as organic solvent based solutions or emulsions. The type of adhesive used will depend in part on the type of material employed for making the sheath and in part on the type of coating or binding used for making the explosive strand. For cellulosic materials, the preferred adhesives are the carbohydrate types with or without an added organic resin. Representative adhesives of this type can 'be ge-latinized starch, with or without a thermosetting resin, which can be a phenol or resorcinolaldehyde, a urea aldehyde or melamine aldehyde resin. If the latter resins are used, the adhesive is preferably in aqueous emulsion form. Rubber based adhesives can be 'latexes or dispersions of natural or synthetic rubber in an organic solvent, such as benzene or toluene. Pressure sensitive adhesives are included among the rubber base types. Proteinaceous resins can be animal proteins, such as gelatin dissolved in Water, and can contain insolubilizing ingredients such as borax and preservatives.

Organic solvent soluble synthetic resins can also be used as solvents. Representatives are a plasticized polyvinyl chloride in methylethyl ketone or cyclohexanone, or polystyrene in benezene or toluene, or polymethyl or ethyl acvrylates in benezene, an aliphatic ketone or an ester such as methyl or ethyl acetate.

FIGURE 2 shows the presplitting device filled with stemming in position in a borehole ready to be detonated. The explosive strands 14, 14 are in close contact with and in proper placement for splitting rock faces 18, 19 along a line of The explosive device shows water as stemming, which forces the walls 16, 17 of the explosive device against the wall .18, 19 of the borehole. Since the strands 14, 14' are either adhesively secured to or interposed between the walls of the sheath 10, the explosive device can be readily placed in the borehole in proper alignment by tying or sealing off the bottom end, placing some sand, gravel, water or other non-detonable weighting material into the sheath through the open top end and lowering the device and aligning it in the borehole. After proper alignment is attained, the device can be filled with stemming and thus hold the explosive strand in proper position in close contact with the rock surface for fracturing the rock along a predetermined line upon detonation of the explosive.

Detonation can be effected by attaching a cap to the strand and connecting the cap to a source of electric current. Any electrical cap blasting system or cap blasting squibs can be employed for this purpose.

A preferred method for manufacturing the explosive device is shown in FIG. 3, where 22, 22' each represent a roll of a heat sealable plastic film 23, 23 mounted on axles 24, 24 for rotational feeding of films between rotatable heat sealing rollers 25, 26. Concurrently with the feeding of plastic film 23, 23, strands of explosive 27, 27 are fed from rolls 28, 28' to the heat sealing rollers 25, 26 at desired spacing to obtain the proper angular separation in a borehole. The heat sealing rollers are preferably grooved to avoid application of any pressure on the explosive strands, and more preferably, the grooved section of the roll is also cooled to maintain a temperature immediately adjacent the explosive strands appreciably below that at which the plastic films are sealed. The heat sealing section of the roll is maintained at the proper temperature to soften at least one of the plastic films, and at sufficient pressure to cause the sheets to adhere to each other.

Alternately, if the explosive strand is to be bound to the sheet by an adhesive, an adhesive pot having a roller rotating therein is placed under the strands, so that the top of the adhesive containing surface of the roll contacts the under surface of the explosive strand. The heat sealing rolls are replaced with rolls which apply a slight pressure to the composite passing between them or, in place of the pressure rolls, a pair of travelling belts or webs can be used. The adhesively bound device should preferably be passed through a drying chamber where any liquid or solvent used in the adhesive is evaporated. Other sheath materials mentioned above can be employed in the method in place of the plastic film.

After heat sealing or adhering the explosive strands, the explosive device is wound on a roll 29.

It is understood that details of mechanisms for performing the several steps of the method for making the explosive device of this invention are well-known in the art and do not constitute any part of the invention described and claimed herein.

Another method for making the explosive device is to feed the film or textile from rolls, intermittently, to a cutting station located ahead of the heat sealing rollers or pressure belt described above. By this means, the sheath material and explosive strands can be cut to any predetermined length with properly positioned elements, so that one end of the sheath can be heat sealed or adhesively secured and the other end can remain open. The explosive strands can be spaced their desired distance from each other and one end of each strand can extend beyond the open end of the sheath to provide for attachment of a detonating cap.

An advantage of having the explosive device in roll form is that proper lengths can readily be prepared for various depths of boreholes. Thus, a length slightly greater than the borehole is cut from the roll. A small amount of the sheath is removed from the end which is to project above the borehole to expose a small length of explosive strand for attachment of the detonating cap. The opposite end is cut longitudinally along dotted lines 30, 30 and transversely along dotted lines 31, 31' of FIG. 1, with care not to cut through seals or bonds 12, 12'. The explosive strand is removed from the cut portion, and thus, there is provided a tab or flap in the sheath which can be heat sealed or knotted to hold stemming or weighting material. The exposed strand can serve as the attachment area for a detonating cap for the next succeeding length of explosive device. There is no waste of material and a great degree of operating choice for the user.

I claim:

1. An explosive article which comprises:

(a) a hollow flexible tubular sheath, and

(b) a plurality of explosive strands spaced apart at a predetermined angular distance from each other around the periphery of the sheath; the strands being confined in the sheath against substantial peripheral movement and separated by the hollow space of the sheath.

2. The article of claim 1 in which the sheath comp-rises a heat sealable thermoplastic.

3. The article of claim 1 in which the explosive strand is Primacord.

4. The article of claim 1 in which the sheath comprises a film.

5. The article of claim 3 in which the Primacord is -200 grain.

6. The article of claim 1 having two strands spaced from each other.

7. The article of claim 1 having three strands spaced at 90 intervals.

8. The article of claim 1 in which the sheath is adhesively bonded.

References Cited UNITED STATES PATENTS 3/1959 Rey 10227 l/1964 Karpovitch l0221.6 X 

1. AN EXPLOSIVE ARTICLE WHICH COMRISES: (A) A HOLLOW FLEXIBLE TUBULAR SHEATH, AND (B) A PLURALITY OF EXPLOSIVE STRANDS SPACED APART AT A PREDETERMINED ANGULAR DISTANCE FROM EACH OTHER AROUND THE PERIPHERY OF THE SHEATH; THE STRANDS BE- 